Synthetic polymer resins are used for a vast array of applications. In some applications, polymers can come into contact with or can be a source of undesirable organic materials that can be eluted into the atmosphere, a water supply, or an ingestible material inside a polymeric package. These organic materials may be formed by degradation of the polymer during processing, or may be the result of adding small molecules to the matrix, such as plasticizers or solvents. A polymer matrix may also absorb undesirable organic materials from external sources, or allow these materials to diffuse into the polymer package contents. Additionally, the barrier properties of a polymer may cause a buildup of undesirable organic materials inside packaging when, for example, foods inside begin to decay.
One industrially important polymer is polyethylene terephthalate (PET). PET packaging materials in the form of films, shaped containers, bottles, etc. have been known. Further, rigid, or semi-rigid, thermoplastic beverage containers have been made from preforms that are in turn molded from pellets or chips etc. Biaxially oriented blow molded thermoformed polyester beverage containers are disclosed in J. Agranoff (Ed) Modern Plastics, Encyclopedia, Vol. 16, No. 10A, P. (84) pp. 192-194. These beverage containers are typically made from a polyester, a product of a condensation polymerization. The polyester is typically made by reacting a dihydroxy compound and a diacid compound in a condensation reaction with a metallic catalyst. Dihydroxy compounds such as ethylene glycol, 1,4-butane diol, 1,4-cyclohexane diol and other diol can be copolymerized with an organic diacid compound or lower diester thereof such diacid. Such diacidic reactants include terephthalic acid, 2,6-naphthalene dicarboxylic acid, methyl diester thereof, etc. The condensation/polymerization reaction occurs between the dicarboxylic acid, or a dimethyl ester thereof and the glycol material in a heat driven metal catalyzed reaction that releases water or methanol as a reaction by-product leaving, a high molecular weight polyester material. Bulk resin is formed as a convenient flake, chip or pellet adapted for future thermal processing. Bulk polyester material can be injection blow molded directly into a container. Alternately, the polyester can be formed into an intermediate preform that can then be introduced into a blow-molding machine. The polyester is heated and blown to an appropriate shape and volume for a beverage container. The preform can be a single layer material, a bilayer or a multilayer preform.
Metallic catalysts are used to promote a polymerization reaction between diacid material and the dihydroxy compound. At the beginning of the melt phase, ethylene glycol, terephthalic acid, or ester thereof, and metallic catalysts are added to the reactor vessel. Various catalysts are known in the art to be suitable for the transesterification step. Salts of organic acids with bivalent metals (e.g. manganese, zinc, cobalt or calcium acetate) are preferably used as—direct esterification or trans-esterification catalysts, which in themselves also catalyze the polycondensation reaction. Antimony, germanium and titanium compounds are preferably used as polycondensate catalysts. Catalysts that may be used include organic and inorganic compounds of one or more metals alone or in combination with the above-described antimony, also including germanium and titanium. Suitable forms of antimony can be used, including inorganic antimony oxides, and organic compounds of antimony, such as antimony acetate, antimony oxalate, antimony glycoxide, antimony butoxide, and antimony dibutoxide. Antimony-containing compounds are currently in widespread commercial use as catalysts that provide a desirable combination of high reaction rate and low color formation. Titanium may be chosen from the group consisting of the following organic titanates and titanium complexes: titanium oxalate, titanium acetate, titanium butylate, titanium benzoate, titanium isoproprylate, and potassium titanyl oxalate. Organic titanates are not generally used in commercial production.
At the end of the melt phase, after polymerization is complete and molecular weight is maximized, the product is pelletized. The pellets are treated in solid-state polycondensation to increase intrinsic viscosity in order to obtain bottle resin of sufficient strength. The catalysts typically comprise metallic divalent or trivalent cations.
The treatment of polyester materials containing such catalysts can result in byproduct formation. Such byproduct can comprise reactive organic materials such as an aldehyde material, commonly analyzed as acetaldehyde. The formation of acetaldehyde materials can cause off odor or off taste in the beverage and can provide a yellowish cast to the plastic at high concentrations. Polyester manufacturers have added phosphorus-based additives as metal stabilizers to reduce acetaldehyde formation.
Many attempts to reduce aldehyde formation have also caused problems. Antimony present as Sb+1, Sb+2 and Sb+3 in the polyester as catalyst residues from manufacture can be reduced to antimony metal, Sb0, by the additives used to prevent aldehyde formation or scavenge such materials. Formation of metallic antimony can cause a gray or black appearance to the plastic from the dispersed, finely divided metallic residue.
The high molecular weight thermoplastic polyester can contain a large variety of relatively low molecular weight compound, (i.e.) a molecular weight substantially less than 500 grams per mole as a result of the catalytic mechanism discussed above or from other sources. These compounds can be extractable into food, water or the beverage within the container. These beverage extractable materials typically comprise impurities in feed streams of the diol or diacid used in making the polyester. Further, the extractable materials can comprise by-products of the polymerization reaction, the preform molding process or the thermoforming blow molding process. The extractable materials can comprise reaction byproduct materials including formaldehyde, formic acid, acetaldehyde, acetic acid, 1,4-dioxane, 2-methyl-1,3-dioxolane, and other organic reactive aldehyde, ketone and acid products. Further, the extractable materials can contain residual diester, diol or diacid materials including methanol, ethylene glycol, terephthalic acid, dimethyl terephthalic, 2,6-naphthalene dicarboxylic acid and esters or ethers thereof. Relatively low molecular weight (compared to the polyester resin) oligomeric linear or cyclic diesters, triesters or higher esters made by reacting one mole of ethylene glycol with one mole of terephthalic acid may be present. These relatively low molecular oligomers can comprise two or more moles of diol combined with two or more moles of diacid. Schiono, Journal of Polymer Science: Polymer Chemistry Edition, Vol. 17, pp. 4123-4127 (1979), John Wiley & Sons, Inc. discusses the separation and identification of PET impurities comprising poly(ethylene terephthalate) oligomers by gel permeation chromatography. Bartl et al., “Supercritical Fluid Extraction and Chromatography for the Determination of Oligomers and Poly(ethylene terephthalate) Films”, Analytical Chemistry, Vol. 63, No. 20, Oct. 15, 1991, pp. 2371-2377, discusses experimental supercritical fluid procedures for separation and identification of a lower oligomer impurity from polyethylene terephthalate films.
Foods or beverages containing these soluble/extractables derived from the container, can have a perceived off-taste, a changed taste or even, in some cases, reduced taste when consumed by a sensitive consumer. The extractable compounds can add to or interfere with the perception of either an aroma note or a flavor note from the beverage material. Additionally, some substantial concern exists with respect to the toxicity or carcinogenicity of any organic material that can be extracted into beverages for human consumption.
The technology relating to compositions used in the manufacture of beverage containers is rich and varied. In large part, the technology is related to coated and uncoated polyolefin containers and to coated and uncoated polyester that reduce the permeability of gasses such as carbon dioxide and oxygen, thus increasing shelf life. The art also relates to manufacturing methods and to bottle shape and bottom configuration. Deaf et al., U.S. Pat. No. 5,330,808, teach the addition of a fluoroelastomer to a polyolefin bottle to introduce a glossy surface onto the bottle. Visioli et al., U.S. Pat. No. 5,350,788, teach methods for reducing odors in recycled plastics. Visioli et al. disclose the use of nitrogen compounds including polyalkylenimine and polyethylenimine to act as odor scavengers in polyethylene materials containing a large proportion of recycled polymer.
Wyeth et al., U.S. Pat. No. 3,733,309, show a blow molding machine that forms a layer of polyester that is blown in a blow mold. Addleman, U.S. Pat. No. 4,127,633, teaches polyethylene terephthalate preforms which are heated and coated with a polyvinylidene chloride copolymer latex that forms a vapor or gas barrier. Halek et al., U.S. Pat. No. 4,223,128, teach a process for preparing polyethylene terephthalate polymers useful in beverage containers. Bonnebat et al., U.S. Pat. No. 4,385,089, teach a process for preparing biaxially oriented, hollow thermoplastic shaped articles in bottles using a biaxial draw and blow molding technique. A preform is blow molded and then maintained in contact with hot walls of a mold to at least partially reduce internal residual stresses in the preform. The preform can be cooled and then blown to the proper size in a second blow molding operation. Gartland et al., U.S. Pat. No. 4,463,121, teach a polyethylene terephthalate polyolefin alloy having increased impact resistance, high temperature, dimensional stability and improved mold release. Ryder, U.S. Pat. No. 4,473,515, teaches an improved injection blow molding apparatus and method. In the method, a parison or preform is formed on a cooled rod from hot thermoplastic material. The preform is cooled and then transformed to a blow molding position. The parison is then stretched, biaxially oriented, cooled and removed from the device. Nilsson, U.S. Pat. No. 4,381,277, teaches a method for manufacturing a thermoplastic container comprising a laminated thermoplastic film from a preform. The preform has a thermoplastic layer and a barrier layer which is sufficiently transformed from a preformed shape and formed to a container. Jakobsen et al., U.S. Pat. No. 4,374,878, teach a tubular preform used to produce a container. The preform is converted into a bottle. Motill, U.S. Pat. No. 4,368,825; Howard Jr., U.S. Pat. No. 4,850,494; Chang, U.S. Pat. No. 4,342,398; Beck, U.S. Pat. No. 4,780,257; Krishnakumar et al., U.S. Pat. No. 4,334,627; Snyder et al., U.S. Pat. No. 4,318,489; and Krishnakumar et al., U.S. Pat. No. 4,108,324, each teach plastic containers or bottles having preferred shapes or self-supporting bottom configurations. Hirata, U.S. Pat. No. 4,370,368, teaches a plastic bottle comprising a thermoplastic comprising vinylidene chloride and an acrylic monomer and other vinyl monomers to obtain improved oxygen, moisture or water vapor barrier properties. The bottle can be made by casting aqueous latex in a bottle mold, drying the cast latex or coating a preform with the aqueous latex prior to bottle formation. Kuhfuss et al., U.S. Pat. No. 4,459,400, teach a poly(ester-amid) composition useful in a variety of applications including packaging materials. Maruhashi et al., U.S. Pat. No. 4,393,106, teach laminated or plastic containers and methods for manufacturing the container. The laminate comprises a moldable plastic material in a coating layer. Smith et al., U.S. Pat. No. 4,482,586, teach a multilayer of polyester article having good oxygen and carbon dioxide barrier properties containing a polyisophthalate polymer. Walles, U.S. Pat. Nos. 3,740,258 and 4,615,914, teach that plastic containers can be treated, to improve barrier properties to the passage of organic materials and gases, such as oxygen, by sulfonation of the plastic. Rule et al., U.S. Pat. No. 6,274,212, teaches scavenging acetaldehyde using scavenging compounds having adjacent to heteroatoms containing functional groups that can form five or six member bridge through condensation with acetaldehyde. Al-Malaika PCT WO 2000/66659 and Weigner et al., PCT WO 2001/00724 teach the use of polyol materials as acetaldehyde scavengers.
Further, we are aware that the polyester has been developed and formulated to have high burst resistance to resist pressure exerted on the walls of the container by carbonated beverages. Further, some substantial work has been done to improve the resistance of the polyester material to stress cracking during manufacturing, filling and storage. Modifications to the polyester material or formulation used in such an application should not compromise the structural integrity of the formed container.
Beverage manufacturers have long searched for improved barrier material. In larger part, this research effort was directed to carbon dioxide (CO2) barriers, oxygen (O2) barriers and water vapor (H2O) barriers. More recently, original bottle manufacturers have had a significant increase in sensitivity to the presence of beverage extractable or beverage soluble materials in the resin or container. This work has been to improve the bulk plastic with polymer coatings or polymer laminates of less permeable polymer to decrease permeability.
Even with this substantial body of technology, substantial need has arisen to develop biaxially oriented thermoplastic polymer materials for beverage containers that can substantially reduce the elution of reactive organic materials into a food or beverage in the container or reduce the passage of permeants in the extractable materials that pass into beverages intended for human consumption.
Stabilization of polyester resins and absorption of reactive organics such as acetaldehyde have drawn significant attention. Proposals for resolving the problem have been posed. One proposal involves using active stabilizers including phosphor compounds and nitrogen heterocycles as shown in, for example, WO 9744376, EP 26713 and U.S. Pat. No. 5,874,517 and JP 57049620. Another proposal, which has received great attention, includes solid state polycondensation (SSP) processing. The materials after the second polymerization stage are treated with water or aliphatic alcohols to reduce residuals by decomposition. Acetaldehyde may also be scavenged with reactive chemical materials including low molecular weight partially aromatic polyamides based on xylylene diamine materials and low molecular weight aliphatic polyamides.
See, for example, U.S. Pat. Nos. 5,258,233, 6,042,908, and European Patent No. 0 714 832, commercial polyamides see WO9701427, polyethylene imine see U.S. Pat. No. 5,362,784, polyamides of terephthalic acid see WO9728218 and the use of inorganic absorbents such as zeolites, see U.S. Pat. No. 4,391,971.
Bagrodia, U.S. Pat. No. 6,042,908 uses polyester/polyamide blends to improve flavor of ozonated water. Hallock, U.S. Pat. No. 6,007,885, teaches oxygen-scavenging compositions in polymer materials. Ebner, U.S. Pat. No. 5,977,212, also teaches oxygen-scavenging materials in polymers. Rooney, U.S. Pat. No. 5,958,254, teaches oxygen scavengers without transitional catalysts for polymer materials. Speer, U.S. Pat. No. 5,942,297, teaches broad product absorbance to be combined with oxygen scavengers in polymer systems. Palomo, U.S. Pat. No. 5,814,714, teaches blended mono-olefin/polyene interpolymers. Lastly, Visioli, U.S. Pat. No. 5,350,788, teaches method for reducing odors in recycled plastics.
Wood, et al. U.S. Pat. Nos. 5,837,339; 5,882,565; 5,883,161; 6,136,354 and other applications pending, teach the use of substituted cyclodextrin in polyester for barrier properties. Wood et al., U.S. Pat. No. 7,166,671 teach the use of a polymer grafted with cyclodextrin in polyolefins for barrier properties.
Activated carbons (CAS No. 7440-44-0) are porous synthetic solid materials that are commonly used in a wide variety of applications for purification, decolorization, and odor removal of gases and liquids. Activated carbon and in particular acid-washed activated carbon is a highly desirable material to entrain in a polymeric matrix for the purpose of scavenging undesirable organic molecules in gas and liquid phases, such as compounds formed during polymer processing as the products of thermal decomposition. In barrier layer applications, the inclusion of carbon would be desirable for the purpose of including scavenging properties for materials that would otherwise diffuse through the polymer matrix.
However, it is broadly understood that carbon particles are often not used in transparent polymer layers since they can be highly light scattering and can typically provide a black or gray cast to polymer layers. If large enough, individual particles can also be observed when the carbon is present in a clear medium, such as a water-white solvent or polymer matrix. Many ink formulations, for example, employ carbon black as the black pigment of choice. Automobile tires typically employ a large percentage of carbon black. The light scattering properties of carbon, while desirable in some applications, are not desirable where, for example, a clear, water-white, or an opaque or translucent white polymer matrix is desired.
Further, the presence of any particular particle in a polymer matrix can be deleterious to physical properties. Particles can have intimate and strong adhesion to the surrounding polymer matrix. The tensile strength of the polymer matrix typically increases, yet the elongation at break is decreased. Even where matrix-filler interactions are favorable, the resulting physical properties often reflect a lower strain at break than the matrix inherently possesses without the filler due to increased stress per unit of strain. This may be undesirable in certain applications, especially where the tensile properties of the polymer have been optimized without other materials being present. Further, it has been observed that the use of very small amounts of filler particles, such as 0.1 volume fraction or less of the total composition, is actually deleterious to the tensile strength and impact strength, in addition to lowering the elongation at break, where adhesion of the filler to the matrix is good. (For a discussion of this phenomenon see Nielsen, L. E., Simple Theory of Stress-Strain Properties of Filled Polymers, J. Appl. Pol. Sci. 10, 97-103 (1966).)
Where adhesion between the particle and the polymer matrix is minimal, elongation and other tensile properties of the polymer matrix may remain largely the same as the matrix without filler. However, as the matrix is stretched, the lack of adhesion between the particle and the polymer allows the filler to distort and concentrate the stress field by propagating a void around the particle in the direction of the stress. As the polymer breaks the void travels from one filler particle to the next and causes ultimate failure of the polymer.
Variations on these stress-strain behaviors can occur in the melt as well. Thus, a particle in a polymer melt may cause visual defects in the matrix even when particles are so small or used in such a small concentration as to be invisible to the naked eye. Voids may form in the direction of stress as a polymer is biaxially oriented, blowmolded, spun, or some other process that incurs stress to the polymer melt. These voids may be visible to the unassisted human eye as streaks, bubbles, and the like. The visible defects alone may be undesirable, or the defects may undesirable because they constitute weak spots in the polymer matrix, such that the physical properties of the polymer may be compromised in subsequent applications. For example, burst strength of the resulting polymer matrix may in insufficient because the defects cause failure of the matrix under relatively low pressures compared to the polymer without defects. Impact strength, tensile strength, and elongation at break can be similarly affected and may render a polymer matrix unusable for a given application.
Further, many fillers, including carbon, will tend to increase opacity of the otherwise clear, water white polyester. Inclusion of carbon as a filler will typically impart a gray cast, which is undesirable for certain applications e.g. beverage container bottles. However, Otto et al., U.S. Pat. No. 6,358,578, disclose the use of activated carbon in polyester matrixes, where an average particle size of 2 μm or less, preferably 500 nm or less, may be incorporated into polyester without producing discoloration. In that application, carbon particles are cocatalysts in transesterification reactions of the polyester. The carbon particles are milled prior to use in the polyester formulation in order to reduce the particle size. Physical properties of the resulting matrixes are not disclosed, nor are the presence of any structural defects or visual defects aside from discoloration.
Inclusion of activated carbon with cyclodextrin is found in other compositions of the prior art. For example, Nakazima, U.S. Pat. No. 5,001,176 disclose polyolefin compositions having a cyclodextrin and a dibenzylidenesorbitol-type compound. Carbon black is mentioned as an optional additive, but is not claimed. Andrews et al., U.S. Pat. No. 6,790,499 disclose a polyester composition having a polyhydric alcohol, which can be cyclodextrin. Eisenhart et al., U.S. Pat. No. 5,137,571 disclose the use of cyclodextrin as reversibly bound to water soluble polymers for the purpose of reversibly viscosifying aqueous systems. A formulation having carbon black is disclosed, but is not claimed. Nakamura et al., U.S. Pat. No. 5,854,320 disclose an ink composition containing cyclodextrin. Carbon black is disclosed in the specification as a pigment for a blank ink formulation. Similarly, Miyamoto et al., U.S. Pat. No. 6,827,767 and Suzuki et al., U.S. Pat. No. 6,849,111 disclose ink formulations having cyclodextrin and carbon black as a colorant. Woo et al., U.S. Pat. No. 6,833,342 disclose a non-polymeric deodorant composition having cyclodextrin, useful for carpet cleaning applications. Carbon is disclosed in a long list of optional potential additives, but is not claimed.